Half Duplex Research Articles

Network-Assisted Full-Duplex Cell-Free Massive MIMO: Spectral and Energy Efficiencies

We consider network-assisted full-duplex (NAFD) cell-free massive multiple-input multiple-output (CF-mMIMO) systems, where full-duplex (FD) transmission is virtually realized via half-duplex (HD) hardware devices. The HD access points (APs) operating in uplink (UL) mode and those operating in downlink (DL) mode simultaneously serve DL and UL user equipments (UEs) in the same frequency bands. We comprehensively analyze the performance of NAFD CF-mMIMO from both a spectral efficiency (SE) and energy efficiency (EE) perspectives. Specifically, we propose a joint optimization approach that designs the AP mode assignment, power control, and large-scale fading (LSFD) weights to improve the sum SE and EE of NAFD CF-mMIMO systems. We formulate two mixed-integer nonconvex optimization problems of maximizing the sum SE and EE, under realistic power consumption models, and the constraints on minimum individual SE requirements, maximum transmit power at each DL AP and UL UE. The challenging formulated problems are transformed into tractable forms and two novel algorithms are proposed to solve them using successive convex approximation techniques. More importantly, our approach can be applied to jointly optimize power control and LSFD weights for maximizing the sum SE and EE of HD and FD CF-mMIMO systems, which, to date, has not been studied. Numerical results show that: (a) our joint optimization approach significantly outperforms the heuristic approaches in terms of both sum SE and EE; (b) in CF-mMIMO systems, the NAFD scheme can provide approximately 30% SE gains, while achieving a remarkable EE gain of up to 200% compared with the HD and FD schemes.

Covert Rate Study for Full-Duplex D2D Communications Underlaid Cellular Networks

Device-to-device (D2D) communications underlaid cellular networks have emerged as a promising network architecture to provide extended coverage and high data rate for various Internet of Things (IoT) applications. However, because of the inherent openness and broadcasting nature of wireless communications, such networks face severe risks of data privacy disclosure. This paper investigates the covert communications in such networks for providing enhanced privacy protection. Specifically, this paper explores the critical covert rate performance in a full-duplex D2D communication underlaid cellular network consisting of a base station, a cellular user, a D2D pair with a transmitter and a full-duplex receiver, and a warden, where the D2D receiver can operate over either the full-duplex (FD) mode or the half-duplex (HD) mode. We first derive transmission outage probabilities of cellular and D2D links under the FD and HD modes, respectively. Based on these probabilities, we further provide theoretical modelling for the covert rate under each mode and explore the corresponding covert rate maximization by jointly optimizing the transmit powers of the D2D pair and the cellular user. To improve the covert rate performance, we propose a general mode in which the D2D receiver can flexibly switch between these two modes. Under the general mode, we also investigate the theoretical modelling and maximization problems of covert rate. Finally, we present extensive numerical results to illustrate the covert rate performances under the FD, HD, and general modes.

Full-Duplex Communication for ISAC: Joint Beamforming and Power Optimization

Beamforming design has been widely investigated for integrated sensing and communication (ISAC) systems with full-duplex (FD) sensing and half-duplex (HD) communication, where the base station (BS) transmits and receives radar sensing signals simultaneously while the integrated communication operates in either downlink or uplink. To achieve higher spectral efficiency, in this paper, we extend existing ISAC beamforming design to a general case by considering the FD capability for both radar and communication. Specifically, we consider an FD ISAC system, where the BS performs target detection and communicates with multiple downlink users and uplink users reusing the same time and frequency resources. We jointly optimize the downlink dual-functional transmit signal and the uplink receive beamformers at the BS and the transmit power at the uplink users. The problems are formulated under two criteria: power consumption minimization and sum rate maximization. The downlink and uplink transmissions are tightly coupled due to both the desired target echo and the undesired interference received at the BS, making the problems challenging. To handle these issues in both cases, we first determine the optimal receive beamformers in closed forms with respect to the BS transmit beamforming and the user transmit power. Subsequently, we invoke these results to obtain equivalent optimization problems and propose iterative algorithms to solve them. In addition, we consider a special case under the power minimization criterion and propose an alternative low complexity design. Numerical results demonstrate that the optimized FD communication-based ISAC brings tremendous improvements in terms of both power efficiency and spectral efficiency compared to the conventional ISAC with HD communication.

Physical layer security based on full duplex and half-duplex multi relay assisted OFDM system

ABSTRACT Broadcasting in wireless channels causes security vulnerabilities since both the intended receiver and the eavesdropper may receive the information. Physical layer security (PLS) ensures the confidentiality of information transmitted wireless medium, even in the presence of eavesdroppers, without relying on cryptographic techniques implemented at higher layers. A PLS method for cooperative relay based Orthogonal Frequency Division Multiplexing (OFDM) with optimal relay selection and power optimization is proposed. In order to increase the overall system’s secrecy rate, a hybrid relaying and water filling based optimal power allocation is performed for multi-relay assisted OFDM-based wireless networks. By changing the eavesdroppers’ distances, the performance efficiency of the proposed system is verified. The analysis is carried out for both Full Duplex (FD) and Half Duplex (HD) systems and their performances are compared with existing equal power allocation technique. The proposed method combines relay selection and novel power optimization process to improve secrecy rate than the existing power allocation methods for both HD and FD systems.

Downlink power control in C-RAN enabled full duplex cellular networks

Full duplex (FD) in cloud radio access networks (C-RAN) has improved the overall system throughput at most to double the half duplex (HD) counterpart. Although there is an overall improvement in the throughput, it is mainly due to the downlink (DL) rate, while the uplink (UL) rate is highly degraded due to the substantial DL interference. In this paper, we showed how by employing a downlink power control (DLPC), the overall capacity could be improved along with UL rate improvement. In DL, we could achieve 2.9 times the HD rate and 1.5 times that of FD without DLPC. In UL, 1.6 times the HD rate and the improvement up to 3.49 bps/Hz from rates of the order 10−4 bps/Hz of FD without DLPC. We have also shown how by appropriately selecting DL and UL power control parameters, we can reduce the cluster size requirement in the FD C-RAN system and the fronthaul capacity requirements. We use Matern Cluster Process (MCP) to model the network. We provide coverage and rate as integral expressions in terms of special functions and algebraic terms. We also derive closed-form approximations for asymptotic rates and reflect few insights into the system design.

Outage probability and error rate analysis of full duplex relay in asymmetric fading channels

SummaryFull duplex (FD) technique has evolved as a viable solution to address the spectrum scarce issue. It has gained research interest for its potential to double the wireless link capacity and enhance spectral efficiency (SE). In this paper, the end‐to‐end performance of an amplify‐and‐forward full duplex relay(FDR) in asymmetric Rayleigh–Rician fading channels is explored, unlike the other works that assume symmetric fading conditions in both the links. The asymmetric or mixed fading channels properly model the realistic communication scenarios like satellite/terrestrial wireless communication systems. In this work, we consider that the source‐relay link experiences Rayleigh fading and the relay‐destination link experiences Rician fading. The novel exact and lower bound closed form analytical expressions for outage probability (OP) and bit error rate (BER) for the considered FD system are derived. Moreover, the effect of severity of fading and the amount of residual self‐interference (RSI) on the performance of FDR are also studied. In addition, MC simulations are carried out to validate the results. It is observed that the performance metrics, OP and BER, are highly dependent on the severity of fading and the amount of RSI. Furthermore, it is found that typically at the SNR of 10 dB, an improvement of approximately 27.6% in OP is obtained. Also, our work offers appreciable SNR gain, for example, for a BER of 10−2, an SNR improvement of around 11 dB is achieved. These findings have been compared with the mixed Rayleigh–Rician fading channel conditions considering only half duplex(HD) mode. These parameter metrics are helpful in analyzing the performance of FD in various communication scenarios such as LoS/NLoS conditions and hence pave the way for more realistic FDR.

On the Capacity Analysis Performance of ASIC Based Hybrid Full and Half Duplex User Relaying Cooperative NOMA System

On the Capacity Analysis Performance of ASIC Based Hybrid Full and Half Duplex User Relaying Cooperative NOMA System

C-FD MAC: Constellation based Full-Duplex MAC protocol

Simultaneous transmission and reception of data packets in Full-Duplex (FD) communication can theoretically double the system throughput. However, efficient self-interference mitigation and symbol detection at the receiver is required to realize the full potential of FD communication in practical scenarios. In this paper, we propose a constellation-based FD medium access control (MAC) protocol (C-FD) for wireless local area networks (WLAN). In the proposed C-FD MAC protocol, the node and Access Point (AP) can exchange packets simultaneously by transmitting the symbols and using different modulation schemes. The superimposed constellation diagram has been used to decode the symbols efficiently at both ends. The novel feature of the C-FD MAC protocol is that it does not require any complicated interference cancellation techniques. The analytical results for Symbol Error Rate (SER), Packet Error Rate (PER), and throughput have been derived for the symmetrical and asymmetrical FD link considering the additive white Gaussian noise (AWGN) with Rayleigh fading. The proposed C-FD MAC protocol achieves nearly twice the throughput compared to Half duplex (HD) communication without compromising the SER. The analytical results have been validated with extensive simulation.

Half-duplex and full-duplex interference mitigation in relays assisted heterogeneous network.

In a multicell environment, the half-duplex (HD) relaying is prone to inter-relay interference (IRI) and the full-duplex (FD) relaying is prone to relay residual-interference (RSI) and relay-to-destination interference (RDI) due to Next Generation Node B (gNB) traffic adaptation to different backhaul subframe configurations. IRI and RDI occur in the downlink when a relay is transmitting on its access link and interfering with the reception of a backhaul link of another victim relay. While the simultaneous transmission and reception of the FD relay creates the RSI. IRI, RDI, and RSI have detrimental effects on the system performance, leading to lower ergodic capacity and higher outage probability. Some previous contributions only briefly analysed the IRI, RSI, and RDI in a single cell scenario and some assumed that the backhaul and access subframes among the adjacent cells are perfectly aligned for different relays without counting for IRI, RSI and RDI. However, in practise the subframes are not perfectly aligned. In this paper, we eliminate the IRI, RSI, and RDI by using the hybrid zeroforcing and singular value decomposition (ZF-SVD) beamforming technique based on nullspace projection. Furthermore, joint power allocation (joint PA) for the relays and destinations is performed to optimize the capacity. The ergodic capacity and outage probability comparisons of the proposed scheme with comparable baseline schemes corroborate the effectiveness of the proposed scheme.

Performance Analysis of Full Duplex Bidirectional Machine Type Communication System Using IRS with Discrete Phase Shifter

In this paper, passive Intelligent Reflecting Surface (IRS) is used to enhance the performance of a Full Duplex (FD) bidirectional Machine Type Communication (MTC) system with two source nodes. Each node is equipped with two antennas to operate in FD mode. In reality, self-interference and discrete phase shifting are two major impairments in FD and IRS-assisted communication, respectively. The self-interference at source nodes operating in FD mode is mitigated by increasing the number of meta-surface elements at the IRS. Bit Error Rate (BER) and outage performances are analyzed with continuous phase shifting and discrete phase shifting in IRS. Closed-form analytical expressions are derived for the outage probability and BER performances of the IRS-assisted bidirectional FD-MTC system with a continuous phase shifter. The outage and BER performances of the IRS-assisted bidirectional MTC system in the FD mode have Signal-to-Noise Ratio (SNR) improvement compared with the IRS-assisted bidirectional MTC system in Half Duplex (HD) mode, as the number of reflecting elements in IRS is doubled in the FD mode. The outage and BER performances are degraded by a discrete phase shifter. Hence, performance degradation of the proposed IRS-assisted bidirectional FD-MTC is examined for 1-bit shifter (0, π), 2-bit shifter (0, π/2, π, 3π/2), and for 3-bit shifter (0, π/4, π/2, 3π/4, π, 5π/4, 3π/2, 7π/4). The performance degradation when a discrete phase shifter is employed in IRS is compared with the ideal continuous phase shifter in IRS. Further, achievable rate analysis is carried out for finding the best location of the IRS in a bidirectional FD-MTC system.

Performance Analysis and Deep Learning Assessment of Full-Duplex Overlay Cognitive Radio NOMA Networks Under Non-Ideal System Imperfections

In this paper, we investigate the effectiveness of an overlay cognitive radio (OCR) coupled with non-orthogonal multiple access (NOMA) system using a full-duplex (FD) cooperative spectrum access with a maximal ratio combining (MRC) scheme under the various non-ideal system imperfections. In view of practical realization, we ponder the impact of loop self-interference, transceiver hardware impairments, imperfect successive interference cancellation, and channel estimation errors on the system performance. We investigate the performance of the proposed system by obtaining closed-form expressions for outage probability and ergodic rate for primary as well as secondary users using Nakagami-m fading channels. As a result, we reveal some notable ceiling effects and present efficacious power allocation strategy for cooperative spectrum access. We further evaluate the system throughput and ergodic sum-rate (ESR) to assess the system’s overall performance. Our findings manifest that the FD-based OCR-NOMA can comply with the non-ideal system imperfections and outperform the competing half-duplex (HD) and orthogonal multiple access (OMA) counterparts. Due to the massive complexity of the suggested system model, direct derivation of the closed-form formula for the ESR becomes cumbersome. To address this problem, we develop a deep neural network (DNN) framework for ESR prediction in real-time situations.

Performance Analysis of Full-Duplex Multirelaying Energy Harvesting Scheme in Presence of Multiuser Cognitive Radio Network

This paper investigates the outage performance of secondary receiver with an energy harvesting cognitive radio network employing multiple full-duplex (FD) relaying protocol in presence of multi-user spectrum sharing environment. Under this energy harvesting aided FD relaying network scenario, adaptive transmit power policies for the secondary user (SU) source, secondary FD relays and exact outage probability of the secondary user are derived analytically in presence of multiple primary users and multiple secondary destinations. Impact of self interference at the receive antenna of each FD relay in addition to all the transmitting interference at all receive nodes is being addressed. A comparative study considering all the interference together in an FD relaying protocol with that of conventional half-duplex (HD) relaying protocol is carried out. With the same diversity order, a trade-off between FD multi-relay and multi-destination is shown. Closed form expressions of secondary outage probability for FD energy harvested relay equipped CR network has also been evaluated. Maintaining quality of service (QoS) of multiple primary users (PUs), power allocation strategies at each secondary transmitting node is taken care of. Finally, all the analytical closed form expressions have been validated through Monte-Carlo simulations.

Joint selection of FD/HD and AF/DF for covert communication in two-hop relay systems

This paper focuses on the covert communication in a two-hop relay system consisting of a transmitter, a relay, a receiver and a warden, where the relay can flexibly select between the transmission modes of full-duplex (FD)/half-duplex (HD) as well as between the forwarding modes of amplify-and-forward (AF)/decode-and-forward (DF). For a given combination of transmission mode and forwarding mode, we first provide theoretical modeling for the covert outage probability, transmission outage probability and covert rate. Under such a combination, we then explore the optimal designs of the transmitter transmission rate and the relay transmit power for covert rate maximization, subjecting to the constraints of covert outage probability and upper bound on relay transmit power. Finally, we provide extensive numerical results to illustrate the performance comparison among different combinations of transmission mode and forwarding mode, and how to jointly select a proper combination of transmission mode and forwarding mode to achieve the maximum covert rate in a relay system with given settings of transmitter transmission rate, self-interference coefficient of FD, constraints of covert outage probability, and upper bound on relay transmit power.

Full-duplex multi-user MIMO communication systems performance optimization using leakage-based precoding

The spectral efficiency (SE) can approximately double when using full-duplex (FD) multiuser MIMO communications. However, there are difficulties because of multiuser interferences, self-interference (SI), and co-channel interference (CCI). To improve the SE of the downlink (DL), this paper proposes CCI-aware enhancement to SLNR (signal-to-leakage-and-noise-ratio) signal-to-leakage-and-noise-ratio (SLNR). It considers a suppressing filter at the receiver to cancel the interferences again designing a beamformer based on CCI-plus-noise covariance matrices for every user at the transmitting side. Additionally, we propose an improvement in the SLNR method by using SI-plus-noise covariance matrices to design uplink (UL) beamformers. Unlike zero-forcing and block-diagonalization, the SLNR approach serves numerous antennas at users and BS (base station). The total SE of the communication yielded using the optimized precoder, i.e., obtained from the SLNR-based precoding. To achieve maximum energy efficiency (EE), we use a power consumption model. Simulation results confirm that full-duplex performs well compared to half-duplex (HD) when the number of antennas at every user in uplink as well downlink channels grow, for all Rician factors, for slight powers of the CCI and SI, and a limited number of antennas at the BS. With the proposed scheme for given transmit power and circuit power, we demonstrate that FD has a higher EE than HD.

In band full duplex (IBFD) technology for next generation wireless networks: A survey in cellular networks

Next-Generation (NextG) wireless communication networks with their widespread applications require high data rates, seamless connectivity and high quality of service (QoS). To cope up with an unprecedented rise of data hungry applications, users demand more spectral resources imposing a limitation on available wireless spectrum. One of the potential solutions to address the spectrum scarce issue is to incorporate in band full duplex (IBFD) or full duplex (FD) paradigm in next generation networks including 5G new radio (NR). Recently, FD has gained the research interest in cellular networks for its potential to double the wireless link capacity and enhancing spectral efficiency (SE). In half duplex (HD) cellular networks, base stations (BSs) can either perform uplink (UL) or downlink (DL) transmission at a particular time instant leading to reduced throughput levels. Due to the advancement in the self interference reduction (SIR) techniques, full duplex base stations (FD-BSs) can be employed to allow simultaneous UL and DL transmissions at the same time-frequency resources as compared to its HD counterpart. It ideally achieves twice the throughput without any additional complexity at user-equipment(UE). This paper covers a detailed survey on FD cellular networks. A series of SIR approaches, UE-UE mitigation techniques are summarized. Various existing MAC protocols and antenna architectures for FD cellular networks are outlined. An overview of security aspects for FD in cellular networks is also presented. Lastly, various open issues and possible research directions are brought up for FD cellular networks.

Performance analysis of hybrid half and full duplex user relaying non orthogonal multiple access system with advanced successive interference cancellation

Performance analysis of hybrid half and full duplex user relaying non orthogonal multiple access system with advanced successive interference cancellation

Full-duplex underwater acoustic communications via self-interference cancellation in space

Traditionally, underwater acoustic communications are half-duplex (HD), i.e., the hydrophones and transducers operate in non-overlapping time-slots/frequency-bands in one direction. To double the spectral efficiency into the full-duplex (FD) mode, which transmit and receive signals simultaneously, a self-interference cancellation (SIC) technique in space is introduced and deployed. Specifically, a novel underwater acoustic system is proposed to perform FD-SIC efficiently via an integrated design combining underwater acoustic vector sensor (AVS) and phased array transducer (PAT) to realize the spatial SIC. The energy focusing function of the beamformer (BF) helps PAT avoid self and mutual spatial interference. The AVS keeps updating the direction of arrival information to let BF adjust the steering angle via an adaptive protocol. The field-programmable gate array (FPGA) Direction of Arrival Estimation (DOA) estimation is done by a 12-element AVS, run-time is 1.22×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> s by MUSIC method, which is promising for real-time applications. In this work, phase-shift keying (PSK) and PSK-based orthogonal frequency-division multiplexing (OFDM) are deployed as the FD transmission modulation methods in the spacial SIC. The proposal is evaluated and verified via both simulations and emulations in real underwater acoustic channels collected in the Gulf of La Spezia, Italy, and it is able to achieve 59 dB SIC while modulating with binary phase-shift keying (BPSK) with carrier wave frequency 80 kHz and AVS steering angle −5°. Moreover, it has at least 37 dB SIC within the steering angle region.

Intelligent-Reflecting-Surface-Aided Bidirectional Full-Duplex Communication System With Imperfect Self-Interference Cancellation and Hardware Impairments

In this article, we combine two new technologies [full-duplex (FD) transmission and intelligent reflecting surface (IRS)] in a wireless communication system for investigation. Specifically, we evaluate the performance of an IRS-aided bidirectional FD communication system in a practical scenario where imperfect self-interference (SI) cancellation and hardware impairments (HIs) are taken into consideration. We successfully derive the closed-form expressions of ergodic capacity (EC) and symbol error rate (SER) of the IRS-aided FD-HI system over Rayleigh fading channels. We confirm the correctness of the derived expressions via Monte-Carlo simulations. To clarify the effects of residual SI and HIs, we compare the performance of the IRS-aided FD-HI system with that of the IRS-aided FD-ideal hardware (ID), half-duplex (HD)-HI, and HD-ID systems. Numerical results clarify a strong impact of residual SI and HIs on the EC and SER of the IRS-aided FD-HI system. Thus, the EC and SER of the IRS-aided FD-HI system go to the saturated values in a high signal-to-noise regime even with a large number of reflecting elements in the IRS. Therefore, depending on the residual SI and HI levels as well as the requirements about the EC and SER in practice, we can use appropriately the transmit power of terminals and number of reflecting elements in the IRS for enhancing the performance and saving the energy consumption of the IRS-aided FD-HI system.

System-Level Analysis of Full-Duplex Self-Backhauled Millimeter Wave Networks

Integrated access and backhaul (IAB) facilitates cost-effective deployment of millimeter wave (mmWave) cellular networks through multihop self-backhauling. Full-duplex (FD) technology, particularly for mmWave systems, is a potential means to overcome latency and throughput challenges faced by IAB networks. We derive practical and tractable throughput and latency constraints using queueing theory and formulate a network utility maximization problem to evaluate both full-duplex (FD)-IAB and half-duplex (HD)-IAB networks. We use this to characterize the network-level improvements seen when upgrading from conventional HD IAB nodes to FD ones by deriving closed-form expressions for (i) latency gain of FD-IAB over HD-IAB and (ii) the maximum number of hops that a HD- and FD-IAB network can support while satisfying latency and throughput targets. Extensive simulations illustrate that FD-IAB can facilitate reduced latency, higher throughput, deeper networks, and fairer service. Compared to HD-IAB, FD-IAB can improve throughput by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times $ </tex-math></inline-formula> and reduce latency by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times $ </tex-math></inline-formula> for a fourth-hop user. In fact, upgrading IAB nodes with FD capability can allow the network to support latency and throughput targets that its HD counterpart fundamentally cannot meet. The gains are more profound for users further from the donor and can be achieved even when residual self-interference is significantly above the noise floor.

Cooperative Non-Orthogonal Multiple Access Transmission Through Full-Duplex and Half-Duplex Relays

We investigate the beamforming for cooperative non-orthogonal multiple access (NOMA) transmission through a decode-and-forward relay either with full-duplex (FD) mode or with half-duplex (HD) mode. The beamforming vectors at the source and at the relay are optimized to maximize the end-to-end sum rates of the NOMA transmission. The optimal beamforming for the second-hop of the NOMA transmission is present, from which the beamforming algorithms for the two relay modes are derived. For the FD case, the removal of self interference from the feedback loop is important and a two dimensional (2-D) search algorithm based on semi definite relaxation (SDR) is provided, where the 2-D search range is narrowed down as the algorithm iterates. For the HD mode, no iteration is necessary and only one implementation of SDR is required since the SI suppression is not needed. Simulation results show the performance advantage of the proposed FD mode system over that of HD mode in various parameter settings. This justifies the cost and complex hardware circuitry of FD mode.